1. Field of the Invention
The present invention relates to new methods and systems for analyzing a variety of physical characteristics of a photoresist composition. More particularly, xe2x80x9cin-linexe2x80x9d analysis methods and systems are provided that can enable effective monitoring of a resist coating layer, particularly after exposure to activating radiation, but prior to any post-exposure bake or development steps. Monitoring is preferably accomplished by spectroscopic analysis of a resist coating layer, preferably by measuring fluorescence of the coating layer. Resists of the invention preferably contain a component that can facilitate monitoring, such as a proton-acceptor compound,
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that arc opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition, Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4.
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Enhanced resist resolution may not be achieved by the resist composition itself. In particular, the various lithographic processing tools, the processing environment and the like all can directly impact the resolution of the processed resist.
We now provide new methods for analysis of photoresist coating layers. Preferred methods of the invention include fluorescence microscopy inspection of an imaged resist layer prior to any type of development processing. Thus, the quality and potential resolution of a latent image patterned in the resist layer can be evaluated prior to incurring the time and expense of further processing of the resist.
Specifically preferred aspects of the invention provide fluorescence techniques for detection of latent photoacid images in photoresists, including chemically amplified resists. The results of the analysis then may be used to directly calibrate or otherwise adjust the exposure apparatus used to image to resist, thereby enabling production of developed relief images of enhanced resolution and a consistent lithographic process.
Preferred resists for use in the methods of the invention contain a component that facilitates monitoring of a resist coating layer, particularly a component that can function as a proton acceptor and exhibit a change is fluorescence upon exposure to photogenerated acid. Suitable components include aromatic compounds that have a moiety that can accept a proton such as an amine or other basic group that can serve as a proton acceptor.
Particularly preferred methods of the invention include applying a resist coating layer onto a substrate surface, e.g. a microelectronic wafer surface; exposing the applied resist layer to patterned radiation activating for the resist (e.g., generates photoacid in the resist); monitoring the exposed resist layer e.g. by spectroscopic analysis, particularly fluorescence microscopy; and thereafter further processing the resist layer as desired such as by post-exposure bake (PEB) and development steps. Additionally, if after the monitoring step the resist layer and latent relief image are unsatisfactory, the resist layer simply car be removed and the substrate re-processed, rather than conducting further, unwarranted lithographic processing.
The developed resist image also can be further analyzed if desired, e.g. by scanning electron microscopy (SEM) or the like.
As discussed above, in preferred aspects, methods of the invention provide for fluorescence detection of latent photoacid images to calibrate the focus of a projection lithography system. As discussed, the methods can be employed as a fabrication line diagnostic (specifically with regard, but not limited, to focus validation), where assessment can be conducted aver exposure step with no need to proceed through PEB and/or development.
A wide variety of photoresists can be employed in the methods of the invention. Preferred photoresists for use in the methods of the invention are chemically amplified, positive acting resists such as those resists that contain a resin with photoacid-labile groups and one or more photoacid generator compounds. Conventional positive resists also may be employed in the resists of the invention, in particular positive resists that do not contain a deblocking resin, e.g. diazonaphthoquinone photoactive component and a resin such as a novolak resin. Negative photoresists also may be employed in the methods of the invention.
Preferred photoresists for use in the methods and systems of the invention are chemically-amplified photoresists that are imaged at relatively short wavelengths such as sub-300 nm and sub-200 nm. For sub-300 nm imaging, such as 248 nm imaging, preferred photoresists include those that contain a phenolic polymer, particularly a phenolic/acrylate copolymer where the acrylate may contain photoacid-labile groups such as provided by polymerization of tert-butylacrylate or tert-butyl-methacrylate. For sub-200 nm imaging such as 193 nm imaging, preferred photoresists will contains a resin that is substantially (e.g. less than 5, 4, 3, 2 or 1 mole percent based on total polymer units) free of aromatic units such as phenyl. A particularly preferred resin for use in a resist imaged at 193 nm comprises a heteroalicyclic ring or carbon alicyclic ring (i.e. non-aromatic has all carbon ring members such as norbornyl) fused to the polymer backbone. Such photoresists disclosed in U.S. Pat. No. 6,306,554 to Barclay et al. For imaging at 157 nm, a photoresist that contains a fluorocarbon resin is preferred.
A variety of exposure wavelengths may be employed in the systems and methods of the invention, including sub-300 nm exposures such as 248 nm, and sub-200 nm exposures such as 193 nm, 157 nm and the like.
We have found that extremely small imaged features can be visualized well with methods and systems of the invention. In particular, we have found that sub-300 nm and sub-200 nm features patterned in a resist coating layer can be visualized well with the fluorescence methods of the invention.
Other aspects of the invention are disclosed infra.